Paper manufacture



Sept. 26, 1961 c. E. AHLM, JR; ET AL 3,001,887

PAPER MANUFACTURE Filed Sept. 20, 1957 IN VENTORS mm A. A #1 M, (/2, [A A! a m (ya/ 19mm ms.

United States Patent 3,001,887 PAPER MANUFACTURE Carl E. Ahlm, Jr., and Earl B. Brookbank, Jr., Chillicothe, Ohio, assignors to The Mead Corporation, Dayton, Ohio, a corporation of Ohio Filed Sept. 20, 1957, Ser. No. 685,067 4 Claims. (Cl. 117-1) This invention relates to paper manufacture and especially to improved paper to be used for agreements, stock certificates, coupons, insurance policies, revenue stamps, bonds, money orders, tickets for the distribution of prizes, and the like, which may be readily authenticated Where it is desired to prevent unauthorized duplication or coun terfeiting thereof. More particularly, this invention relates to paper documents and the like, inherently embody-; ing a concealed property for providing a word, symbol or; design which may be developed at any time to prove the authenticity of the document. 4

Accordingly, it is an object of this invention to provide a paper which has the appearance of ordinary, paper or the like and which has no indication to forewarn counterfeiters or others of its potential authentication character: istic. I

Another object of this invention is to provide such a paper which may be economically manufactured and which will possess a normal conventional appearance, the special character of which is concealed even by chemical analysis. A further object is to provide such a paper having a surface thereof printed with a sensitive, indistinguishable material which Will form initially colorless and inherently authenticating words, symbols or designs adapted to be conspicuously developed in color upon the application of certain chemical agents.

A further object of this invention is to provide a protective paper or the like which will serve as a deterrent to. counterfeiting or dishonesty.

Still another object is to provide an authentication paper without sacrificing other desirable properties of the paper.

Other objects and advantages will become apparent from the following description and appended claims, it being understood, however, that various changes may be made by those skilled in the art without departing from the scope of this invention.

The single figure of the accompanying drawing schematically shows a paper document of this invention embodying a latent printing which has been partially developed to prove the authenticity of the document.

The authentication paper of this invention is produced by treating ordinary writing, book or magazine paper with a colloidal silica which because of its small particle size is substantially colorless so that when applied as an aqueous sol to the paper and thereafter dried, its presence thereon is normally invisible. While the colloidal silica may be applied to the paper after the paper has been formed into a web, as a coating thereon, it has been found preferable to apply the colloidal silica to paper in the form of a latent printing being thereon, such printing being that of authenticating words, symbols or designs,

and produced on the paper, for example, by means of a printing press. Such latent printing is non-hygroscopic, is v not identifiable under ultra-violet light, but will manifest its printing pattern by organic chemical developing compositions, also provided by this invention. Such develop- Patented Sept. 26, 1961.

. 2 i V 7 ing compositions are preferably colorless solutions of a leuco compound in a suitable solvent and upon application thereof to the paperwhich-has been provided with the latent printing'of this invention, develops ,a conspicu ous color, and the authenticating matter is rendered visible and legible. 1

Previously manufactured papers,- such as for example, bond paper, sulfite paper, cardboard, kraft paper, and' similar papers whichcontain clay as a filler or as a coating may be used for producing the authentication paper of this invention. The colloidal silica as applied on the sur-, face of these papers is preferably incorporated thereon in direct printing form, as discrete particles of less than 0.1,

, micron in particle size so that the formed latent image is refractive and hence invisible.

When preparing the improved paper of this invention for authetication so as to insure the desired features of an invisible marking on the paper which is not discernible, even on close megascopic examination, it has been found that a colloidal silica of particle size less than 0.1 micron, and preferably less than 0.05 micron is especially suitable to insure the desired refractive latent image. The colloidal silica of such small particle size as used to carry out this invention is readily comprehended when considered in correlation to optical hypothesis. For example, maximum scattering of light occurs, in the case of such spherical silica particles at a particle diameter of about 0.25 micron, i.e., at a particle diameter of about one-half the wave length of light. Such scattering of incident light'is caused by multiple reflections and refractions by the particles and their presence on the surface of a paper becomes evident. As the particle diameter is reduced below 0.25 micron, re'- flection of incident light decreases, until, at 0.1 micron, the silica particles reflect very little light, the dominant effect then being refraction. It has been found that a surface print on paper comprising such refracting par-Z ticles of colloidal silica in discrete individual relationship" is not visible by ordinary means, even under critical illumination, provided such particles are substantially free ofcolor. And the colloidal silica preferred for ca'rrying out? this invention is characterized by being almost completely colorless.

Illustrative of a colloidal silica which may be utilized in producing the authenticating paper of this invention is. the commercially available Ludox HS which is made; by E. I. du Pont de Nemours & Co. in accordance with the teachings of the Bechtold and Snyder, US. Patent No. 2,574,902 and Rule, US. Patent No. 2,577,485.

Upon application of certain leuco organic developing, compounds in solution to the treated paper, the normally invisible printing on the paper develops a distinctive, conspicuous color, and the authenticating words, symbols I or designs are rendered visible and legible. The normally colorless solution of such a suitable developing compound, when applied to paper having an invisible colloidalsilica print of this invention, is believed to be preferentially ad-j. sorbed on the surface of the silica print and sequentially converted to a colored form, thereby making thev print visible and proving the authenticity of the paper. Without, unduly limiting the leuco organic compounds which efiect'. color development upon contact with the invisible col-Q loidal paper prints, the following aromatic amines, as' colorless solutions, have been found to be especially suit-- able: Michlers hydrol (bis (p-dimethylaminophenyl) methanol); lactone of malachite green (3,3 bis(4-dimethyl 3 amino phenyl) phthalide); leuco of malachite green (a triphenyl methane dye); lactone of crystal violet (3,3 bis (4dimethyl aminophenyl) 6-dimethylamino-phthalide); and lactone of Rhodamine B (Xanthene-9-o-benzoic acid-3,6 bis diethylamino-9-lactone).

These aromatic amines yield colorless solutions in a non-polar solvent, and were found to develop a desirable colored form on contact with the colloidal silica printed paper of this invention. In preparing these amines for use therewith, benzene was used as the solvent. And as solutions, the leuco of malachite green and malachite green lactone produced a green color, Michlers hydrol and crystal violet lactone produced a blue color, and Rhodamine B lactone produced a red color. Certain of the above compounds, as colorless solutions, notably leuco malachite green and Rhodamine B lactone, are converted to the colored form upon adsorption contact with human skin or other materials such as cellulose, and show the silica printed pattern as a deeply colored print on a lighter background of the same color, but are somewhat messy to handle. Michlers hydrol, malachite green lactone and crystal violet lactone are free of this characteristic and represent preferred materials for the developing composition, being non-staining to the hands, and developing the design as a prominently colored print on a substantially white background, when a white paper is used.

Moreover, these colorless compounds all develop a characteristic color, when applied to paper carrying the surface treatment of this invention, but the preferred compounds remain colorless when applied to ordinary papers. And these compounds may be applied to the treated paper by any convenient means. For example, they may be applied from a stamp pad, a pen or from a conventional inked roller.

Referring to the drawing, 10 indicates a portion of a paper document, one surface of which has been printed with the invisible colloidal silica 11 of this invention to form the repeating pattern of the word valid. 12 indi cates a conventional roller carrying a film of colorless developing solution 13 of this invention, which when brought into contact with the latent printed words, develops the words in color.

It is to be understood that other developing compounds which yield colorless solutions, but change to a color form on contact with the described colloidal silica printed paper, are intended to be included within the scope of the present invention.

The present invention is illustrated in the following examples which are to be construed as exemplary rather than as limiting.

Example 1 This is an example in which ordinary white, uncoated sulfite writing paper containing clay filler and produced on a Fourdrinier paper machine was used.

The colloidal silica which was applied to the surface of this paper was prepared by adding 50 parts by weight of water to 100 parts by weight of Ludox HS. Upon analysis, it was determined that the resultant sol contained 20% colloidal silica as SiO that the silica particles had an average diameter of 0.015 microns and that the viscosity at 25 C. was less than 3.6 centipoises.

This sol was then placed in the ink fountain of a flexographic printing press and applied to the writing paper containing the clay filler by an impression roll having a repeating pattern of the words Puerto Rico together with a circular design.

After such printing, further chemical analysis disclosed that the presence of the printing was masked by the silica which was present in the clay filler, and there was no evidence to show the presence of the colloidal silica.

The treated paper was then brought into contact with a wick-type pen containing a colorless solution of lactone of malachite green whereby the authenticating words 4 Puerto Rico together with the circular design were produced in green color.

Example 2 This is also an example of using the writing paper of Example 1, with the difference that a colloidal silical containing 200 parts by weight of water to parts by weight of Ludox HS was applied by means of a multifountain flexographic printing press in a repeating word pattern to the surface of the paper. The sol contained 10% colloidal silica as SiO the silica particles had an average diameter of 0.015 micron and the viscosity at 25 C. was about 3.0 centipoises.

The results were as follows:

The presence of the printing was masked by the silica present in the clay filler. There was no evidence to show the presence of the colloidal silica. The treated paper when brought into contact with a solution of crystal violet lactone, transferred from a stamp pad, produced the authenticating words in blue color.

Example 3 This is an example of using the writing paper of Example 1, with the difference that a colloidal silica contained 100 parts by weight of Ludox" HS with no addition of water. This sol contained 30% colloidal silica as SiO the silica particles had an average diameter of 0.015 micron and the viscosity at 25 C. was 3.6 centipoises. The procedure and the results were the same as in Example 1. t

The examples are proof that the objects of this invention have been attained.

There are further benefits derived from the use of a colloidal silica whose average particle size is less than 0.1 micron. For example, such fine particles can approach the surface of the paper very closely, and under such conditions, forces of gravitational attraction are of sutlicient magnitude to hold the particles in place without the use of a hinder or adhesive, thus leaving their surfaces more or less completely exposed to enter into a color development interaction with the developing composition. The specific surface of such fine particles is high, amounting to the order of 200 square meters per gram.

While the product and process herein described are for the purpose of illustration only, it is to be understood that the present invention includes all modifications and equivalents which fall within the scope of the invention which is defined by the appended claims.

What is claimed is:

l. A process for rendering a paper article subject to authentication comprising the step of printing an authenticating design on the surface of said article with a colloidal silica containing about 10 to 30% colloidal silica as SiO the silica particles thereon having an average diam eter of about 0.015 to 0.1 micron and being subject to coloration when contacted with lactone of crystal violet in solution to thus color said design and make visible the authenticity of said article.

2. A process for rendering a paper article subject to authentication when lactone of crystal violet in solution is applied to said article comprising the step of printing an authenticating design on the surface of said article with a colloidal silica containing about 10 to 30% colloidal silica as SiO the silica particles thereon having an average diameter of about 0.015 to 0.1 micron and being substantially inactive to develop colorations except with said reactant.

3. A process for authenticating a paper article comprising the steps of printing an authenticating design on the surface of said article with a colloidal silica containing about 10 to 30% colloidal silica as SiO and having the silica particles thereof provided with an average diameter of about 0.015 to 0.1 micron, and applying a colorless organic reactant in solution to said surface of said article to color said particles and thus make said design readily visible for authentication purposes, said colorless organic reactant being selected from the group consisting of Michlers hydrol, lactone of malachite green, leuco of malachite green, lactone of crystal violet, and lactone of Rhodamine B.

4. A process as set forth in claim 3 wherein said colorless organic reactant is lactone of crystal violet.

References Cited in the file of this patent UNITED STATES PATENTS 71,663 Sturgeon Dec. 3, 1867 6 Smith June 30, 1942 Rule Dec. 4, 1951 Wilson June 23, 1953 Steinhardt Oct. 6, 1953 Her Aug. 6, 1957 Adams et a1 Mar. 25, 1958 OTHER REFERENCES 10 her 1951. 

3. A PROCESS FOR AUTHENTICATING A PAPER ARTICLE COMPRISING THE STEPS OF PRINTING AN AUTHENTICATING DESIGN ON THE SURFACE OF SAID ARTICLE WITH A COLLOIDAL SILICA CONTAINING ABOUT 10 TO 30% COLLOIDAL SILICA AS SIO2 AND HAVING THE SILICA PARTICLES THEREOF PROVIDED WITH AN AVERAGE DIAMETER OF ABOUT 0.015 TO 0.1 MICRON, AND APPLYING A COLORLESS ORGANIC REACTANT IN SOLUTION TO SAID SURFACE OF SAID ARTICLE TO COLOR SAID PARTICLES AND THUS MAKE SAID DESIGN READILY VISIBLE FOR AUTHENTICATION PURPOSES, SAID COLORLESS ORGANIC REACTANT BEING SELECTED FROM THE GROUP CONSISTING OF MICHLER''S HYDROL, LACTONE OF MALACHITE GREEN LEUCO OF MALACHITE GREEN, LACTONE OF CRYSTAL VIOLET, AND LACTONE OF RHODAMINE B. 